1. Field of the Invention
The present general inventive concept relates to an image forming device, such as a laser printer or a photocopier, to heat a fixing unit using alternating current (AC) power, and more particularly, to a system and method of controlling a temperature of a fixing unit to reduce an instantaneous heating time of the fixing unit and reduce a flicker characteristic.
2. Description of the Related Art
A general fixing circuit used for laser printers and photocopiers includes a controller determining whether power is supplied to a fixing unit, a triac switching unit for applying alternating current (AC) power to the fixing unit, and a triac driver controlling a triac. The general fixing circuit performs simple temperature control of the fixing unit by receiving AC power from an input power supply and applying the AC power to components of the fixing unit. That is, the controller detects a temperature of the fixing unit using a temperature sensor, outputs a switch-on signal if it is determined that a temperature increase is needed, and applies the AC power to the fixing unit by activating the triac to an on-state at a zero-crossing time in every switching period using a photo triac in response to the switch-on signal.
As described above, in the general fixing circuit, since the controller simply controls the triac switching unit in order to control the temperature of the fixing unit, without having information on the AC power, irregular turn-on timing causes a flicker characteristic due to having no information on a voltage sync angle (or a sync angle between voltage and current) of the AC power. A flicker characteristic is an instantaneously flickering phenomenon of a display device using the same power source as an image forming device.
In addition, to reduce a print ready time, a supply of relatively high power may be needed in an initial warm-up of the fixing unit. However, this power increase causes an excessive inrush current, resulting in a more pronounced flicker characteristic.